Field of the Invention
The present invention relates to thermal transfer sheets that exhibit excellent resistance to organic solvents, excellent printability to a material on which a print is to be applied having unevenness in its surface, and excellent printability for fine lines, which thermal transfer sheets are capable of preventing failures of transfer such as tailing from occurring.
Background Art
A thermofusible transfer system is conventionally known as a printing system using a thermal transfer sheet, which thermofusible transfer system uses a thermal transfer sheet that is carried a colored layer obtained by dispersing a colorant such as a pigment or a dye in wax or a resin on a substrate such as a plastic film. The colored layer is transferred onto a material on which a print is to be applied such as paper or a plastic sheet by applying energy depending on image information using a heating device such as a thermal head. Printing image formed by the thermofusible transfer system has high density and exhibits excellent sharpness and are suitable for recording binary format image such as letters and line drawing.
In addition, according to the thermofusible transfer system, variable information typified by attribute information such as addresses, customer information, numbering, and barcodes can be readily output to and recorded in the material on which a print is to be applied using a computer and a heat transfer printer.
Such a thermal transfer sheet is required to have high adhesiveness to the material on which a print is to be applied and high printability for fine lines. In addition, it is required to prevent failures of transfer such as tailing from occurring at the time of the transfer.
In order to meet the requirement, Patent Document 1 has disclosed a thermal transfer sheet comprising, in the order mentioned, a release layer, a colored layer, and an adhesion layer on its support, wherein the adhesion layer contains a polyester-based resin whose glass transition temperature is not less than 70° C. and not more than 80° C.
Further, in cases where the thermal transfer sheet is used in the environment in which an organic solvent like isopropyl alcohol (IPA) is used, what is required is that letters and the like which are formed by the transfer of the colored layer are not erased by the use of the organic solvent. That is, the thermal transfer sheet is required to have resistance to organic solvents.
However, conventional thermal transfer sheets including the thermal transfer sheet disclosed in Patent Document 1 do not have adequate adhesiveness between the adhesion layer and the material on which a print is to be applied. The adhesion layer does not closely contact with the colored layer in an adequate manner either. The organic solvent seeps in those gaps. Thus, there was room for improvement in terms of the resistance to organic solvents.
In addition, some of the materials on which a print is to be applied have unevenness on their surface; and the thermal transfer sheet is required to have high printability even to the material on which a print is to be applied having unevenness in its surface. Yet, the thermal transfer sheet disclosed in Patent Document 1 did not have adequate printability to a material on which a print is to be applied having unevenness in its surface.